Method for repairing superalloy castings using a metallurgically bonded tapered plug

ABSTRACT

A method of repairing cracks, imperfections, and the like in a cast article. A frusto-conical aperture is created in the article in the location of the crack or imperfection. A mating tapered plug is prepared such that the tapered plug can fit into the aperture so that the sloped side walls of the tapered plug evenly and unilaterally rest on frusto-conical sides of the aperture. The tapered plug is disposed into the aperture, and bonding material is applied between the surfaces of the tapered plug and the aperture, before or after insertion of the tapered plug into the aperture. The article is thereafter heated such that the bonding material joins the surfaces of the tapered plug and the aperture. The outer end of the tapered plug thereafter is polished so that such outer end is approximately level with the article&#39;s outer side in a refinement of the invention, the plug member may be pushed into the aperture such that a controlled interference fit is produced.

This application is a division of application Ser. No. 09/366,303, filedAug. 2, 1999, now U.S. Pat. No. 6,199,746 B1, which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to the field of repair of a cast article, and moreparticularly to repair of a cast article having imperfections.

Certain articles, such as airfoils for the power turbine sections of gasturbines, are constructed of superalloys. Due to the extremetemperatures and stresses to which such cast superalloy articles suchas, airfoils, are exposed, imperfections in cast articles can haveserious consequences. In the case of an airfoil, the control of theairfoil wall's thickness, when an airfoil is cast, is critical to thestrength and life of the airfoil.

More particularly, turbine components such as turbine airfoils aretypically cast as hollow structures with complex cooling passagesinside. The complex cooling passages are desired because thetemperatures of the hot combustion gases directed at the airfoil duringoperation are at or above the melting temperature of the superalloycomposition. The cooling medium may comprise air or steam. In the caseof steam, such steam will typically be under pressure higher thancooling air pressure. The airfoil design is sensitive to airfoil wallthickness control because of these factors. Insufficient thicknessresults in significant creep damage due to high local stresses in areasof reduced thickness (i.e. cross-sectional area), while excessive wallthickness results in fatigue damage due to insufficient cooling of theexterior. An about 0.08″ nominal airfoil thickness is predicted toresult in an airfoil achieving its design life if actual thickness canbe maintained to within about 0.02″ of the nominal thickness.

The directional casting process for superalloy components, such asairfoils, typically utilizes ceramic “bumpers” on core surfaces or moldsurfaces. For a nominal cast wall thickness of about 0.08″+/−0.2″,ceramic bumpers of about 0.06″ in height help control wall thickness bythe geometric constraints provided in the form of the ceramic bumpers. Alarge number of bumpers on each casting reduces the likelihood ofdistortion of the ceramic molds and cores.

After the article is directionally cast, the ceramic bumpers areremoved. The wall of the article will be thin wherever there had beenceramic bumpers. In addition, if the mold and the core had been incontact, there would be a small hole in the article at a contact point,and a corresponding thicker area on the other side of the article.Because variations in wall thickness beyond the design specification ofabout 0.08″+/− about 0.02″ may result in early failure of the airfoil,restoration of wall thickness is needed.

The restoration of wall thickness is complicated by the article geometrywhere, for example, an airfoil. At every airfoil bumper location thereis a unique combination of inner surface and outer surface contours tothe airfoil wall exist. In addition, due to variations in wall thicknesswithin the design specification, no two airfoils will have the same wallthickness profile around the airfoil perimeter or along the airfoillength. An airfoil design can, for example, allow for filler material toproject into the airfoil cooling cavity up to about 0.02″ before suchfiller material results in any detrimental perturbation of the coolantflow. Because the coolant can comprise steam, the inner contour at eachrepair should be reasonably smooth so as not to set up a site forcrevice corrosion. Outer surface contours are less of a concern, sincethe outer surface is easily available for hand blending of the fillermaterial back to the airfoil contour.

In addition to a need to satisfactorily repair articles due todimensional imperfections resulting from the casting process, a furtherneed to repair articles whereby cracks may have developed at a locationon the article during the casting process exists. As well, cracks candevelop in airfoils after they have been in service for a period oftime. Up to now, once a crack or imperfection of sufficient size hasbeen detected, the airfoil would be immediately replaced. If the crackor imperfection could be repaired in such a way that the airfoil couldthereafter withstand the extreme operating conditions in a turbine, thenthe expense of replacing the cracked airfoil with a new airfoil can beavoided.

In addition to dimensional concerns for the repairing of an airfoil wallat weakened locations, the strength of the airfoil should be maintained.Steam can be a cooling medium for an airfoil, and the steam injectedinto the cooling passages under pressure creates a pressure vesseleffect therein. A repair should be able to withstand the interiorpressure and be leak-tight, and also be almost as strong as thesurrounding directional material in terms of strength and resistance tocreep and fatigue.

Airfoils are typically formed of superalloys that can havedirectionally-oriented microstructures to satisfy the mechanicalstrength demands for creep resistance or fatigue resistance to achieve asatisfactory design life. Directionally-oriented microstructures can beproduced using directional solidification processes, which result ineither elongated polycrystalline grains or single crystals.Directionally oriented microstructures may be problematic to the repairof dimensional imperfections and cracks therein, since the repaired areashould have a similarly oriented microstructure of uniform strength.

Accordingly, a need exists for a method to repair a cast article havingan area of imperfection in the form of a non-dimensional wall thickness.A further need exists for a method to repair a cast article having anarea of imperfection, in which the repaired article in the repaired areaof imperfection is capable of withstanding stresses which aresubstantially equal to, or a substantial amount of, the stresses whichwould previously be capable of being withstood in absence of suchimperfection.

Further, a need exists for a method to repair a cast article, such as ahollow airfoil, having an area of imperfection or a crack, wherein theairfoil, at the repaired area of imperfection or crack, is capable ofwithstanding interior pressure. Still further, a need exists for amethod to repair a cast article, such as a hollow airfoil, having adirectionally oriented microstructure and growth axis and an area ofimperfection, in which such airfoil, in the repaired area ofimperfection, has an identically aligned growth axis that permits therepaired area to withstand stresses a substantial portion of thosepreviously capable of being withstood by the airfoil.

SUMMARY OF THE INVENTION

Accordingly, in one aspect of the invention, a method of repairing acast article having an area of imperfection, comprises the steps offorming an aperture in the cast article in the area of imperfection, theaperture having sloped side walls, forming a plug member, the plugmember on an external periphery thereof provided with similarly slopedside walls, adapted to substantially abut a portion of the sloped sidewalls of the aperture when the plug member is disposed (inserted)therein, and inserting the plug member into the aperture. A bondingmaterial is applied between the plug member side walls and aperture sidewalls, either before or after insertion of the plug member into theaperture. Lastly, the article is heated the that the bonding materialbonds the sloped side walls of the plug member to the sloped side wallsof the aperture.

Using a method, as embodied by the invention, an imperfection within acast article, such as a wall of non-dimensional thickness, or a crack,may be effectively drilled out by the formation of an aperture in theplace of the imperfection. By providing an aperture with sloped sidewalls, a plug member with similarly sloped side walls adapted to abut aportion of the sloped side walls of the aperture permits the plug memberwhen disposed into the aperture to substantially and evenly overlie aportion of the sloped walls of the aperture. This feature aids thesubsequent bonding step, since the tapered side walls, create a greatersurface area for bonding than would otherwise be the case if the sidewalls of the aperture were non-tapered and perpendicular to the plane ofthe article. The feature also allows the plug to sit as close to andoverlie the tapered surface to which it will be bonded without having toincrease dimensional tolerances and introducing an undesirable gap,which would otherwise be the case if there were no tapered side wallsand the plug member had to be machined slightly under-dimension to allowinsertion into the aperture.

In another aspect of the invention, a turbine airfoil machining processproduces a surface roughness, for example about 0.002″. Therefore, twomating machined surfaces in contact at mutual high spots can havelocally variable widths in the gaps between their surfaces as wide asabout 0.0004″. To fill a gap of about 0.0004″ however, a rightcylindrical plug would have to be at least about 0.0004″ larger than theaperture, and still be capable of insertion. Pre-shrinkage of theright-cylindrical plug member by pre-cooling may not, depending on thesize of the plug member, be sufficient to reduce the size of the plugmember to allow interference-free insertion into a right cylindricalaperture.

In cases where pre-shrinkage is not sufficient, the force necessarilyinvolved in pushing a right-cylindrical plug member into a rightcylindrical aperture, and the difficulty in aligning theover-dimensioned plug in the aperture can cause damage to the surfacesof both the plug or the aperture. The damage can comprise undesirablescratches or micro-cracks, which could act as crack initiation sites andpropagate under the inherent ambient stresses and lead to failure. Thedamage can also cause undesirable recrystallization upon subsequentheat. Advantageously, a method, as embodied by the invention, forforming an aperture and a plug member provides each having similarlysloped walls, the plug member may be disposed into the aperture and thesides thereof will mutually overlie and evenly abut the sloped sides ofthe aperture without needing to be forced into the aperture.

In another aspect of the invention, the sloped walls of the aperture andplug member allow an interference fit to be created and maintainedbetween the sloped walls of the plug member and the aperture when theplug member is disposed in the aperture. This interference fit iscreated without pre-cooling of the plug member and without thedifficulties inserting an oversized plug in an undersized aperture. Thecreated interference eliminates gaps which may exist due to surfaceirregularities in their respective surfaces as wide as about 0.0004″.The interference fit also increases the bonding of the plug member tothe aperture, and increases the structural integrity of the bond.

In a yet further aspect of the method of the invention, the methodcomprises inserting the plug member into the aperture, applying a forceto the plug member to cause an interference fit between the sloped wallsof the tapered plug and sloped walls of the aperture. This method allowsthe elimination of gaps due to surface roughness, and avoidsdifficulties that would be encountered in attempting to insert anover-dimensioned right cylindrical plug to a right-cylindrical apertureof lesser dimensions for an interference fit. The taper of each of theplug and aperture is sufficiently small so when forcefully inserted inthe aperture, the interference fit will allow the plug member to remaintherein.

Where a cast article to be repaired comprises a directionally-orientedmicrostructure and growth axis, the plug member should be capable ofbeing received in the aperture. Thus, the plug member growth axis isoriented and aligned with the cast article growth axis. Thus, the plugmember and aperture each possess mating engagement means, which matinglyengage and allow insertion of the plug member within the aperture uponalignment of the plug member growth axis with the article growth axis. Astep of inserting the plug member into the aperture comprises aligningthe mating engagement means on the plug member with the correspondingmating engagement means of the aperture, and inserting the plug memberin the aperture.

In another aspect of the invention, a plug member for repair ofimperfections in a cast article comprises a superalloy composition anddirectionally-oriented microstructure. The plug member comprises asubstantially identical superalloy composition and adirectionally-oriented microstructure and growth axis. The plug memberis provided with tapered side wall surfaces extending about itsperiphery and tapered to allow the plug member, when forcibly insertedwithin an aperture, to remain in an interference fit within theaperture. The plug member further possesses mating engagement means tomatingly engage and allow insertion of the plug within the aperture whenthe growth axis of such plug member is aligned with the growth axis ofthe cast article being repaired.

The plug member of the present invention may further comprise bondingmaterial, such as a braze alloy or other bonding material, applied toits tapered surfaces. The bonding material readies it for bonding whenplaced on an aperture and subsequently heated.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only,with reference to embodiments shown in the attached drawings, in which:

FIG. 1 is a perspective view of a cast article namely a hollow turbineairfoil of superalloy composition, having an imperfection in theexterior surface thereof;

FIG. 2 is an enlarged cross-section of the hollow turbine airfoilillustrated in FIG. 1, taken along plan A—A;

FIG. 3 is a perspective view of the hollow turbine airfoil of FIG. 1having the imperfection drilled out by way of creation of an aperturehaving sloped walls in place of the imperfection;

FIG. 4 is an enlarged cross-sectional view of the aperture illustratedin FIG. 3;

FIG. 5 is an enlarged side elevation view of a plug member for repair inwhich the plug member comprises sloped side walls adapted to abutsimilarly sloped side walls of the aperture when inserted in theaperture;

FIG. 6 is an enlarged cross-sectional view of the plug member insertedin the created aperture;

FIG. 7 is a perspective view of a hollow, cast turbine airfoil, ofsuperalloy composition having a directionally solidified microstructurein the direction B—B, further having a curvilinear aperture created inthe airfoil exterior to thereby remove an imperfection in the exteriorof the airfoil;

FIG. 8 is a curvilinear tapered plug member, having sloped walls andhaving a directionally solidified microstructure in the direction B—B,which is alignable with the directionally solidified microstructure ofthe airfoil illustrated in FIG. 7;

FIG. 9 is an enlarged cross-sectional view of the curvilinear taperedplug member of FIG. 8 being inserted into the curvilinear aperture inthe airfoil illustrated in FIG. 7; and

FIG. 10 is an enlarged cross-sectional view of the curvilinear taperedplug member of FIG. 8 inserted into the curvilinear aperture in theairfoil of illustrated FIG. 7, so as to create an interference fit.

DESCRIPTION OF THE INVENTION

A casting process that results in an article requiring repair inaccordance with the present invention will be discussed with referenceto the Figures. FIG. 1 illustrates a cast article, such as an airfoil10, for use in a gas turbine. The airfoil 10 is typically formed of asuperalloy composition having a directional or single crystalmicrostructure. The growth axis 14 of the directional microstructure ofthe airfoil 10 is illustrated in FIG. 2, in the direction of arrows B—Bin FIG. 7.

The thickness for the walls according to a design specification of anairfoil 10 can be, for example, about 0.08″, +/− about 0.02″. Thedirectional microstructure and the design thickness satisfy themechanical demands for the creep resistance and fatigue resistancenecessary to achieve a desired airfoil design life. A directionalmicrostructure may be produced by of directional solidification duringcasting the airfoil 10 along the growth axis 14.

The casting process used to satisfy the requirements for wall controlutilizes ceramic “bumpers” within core surfaces or mold surfaces. Forexample, a ceramic bumper used in the casting of the airfoil can beabout 0.06″ in height to control wall thickness. After the article hasbeen cast, the ceramic bumpers are removed. Locations where ceramicbumpers had been located and removed, are identified by numeral 16 inFIG. 2. At other locations where the mold and the core may have been indirect contact, or a ceramic bumper and the mold may have been in directcontact a small hole 18 in the article's wall exists (FIG. 2). Wherethis hole occurs, there will also be a corresponding thicker area (“C”)on the opposite side of the airfoil 10 (FIG. 2).

In a repair process, as embodied by the invention, areas of reducedthickness in an airfoil's walls are determined. An aperture 22 can bemade at each such area by drilling out the wall material (see FIGS. 3and 4). The aperture 22 is defined to insert a plug member 42 (FIG. 5)at each area 16 and hole 18 to have sufficient wall thickness, forexample, a thickness of about 0.08″+/− about 0.02″.

Repair of an airfoil 10 having a superalloy composition can arise incircumstances other than those related to a casting process. Forexample, an airfoil that has been in service can develop a crack. Torepair a crack, an aperture 22 as made in the airfoil, as illustrated inFIGS. 3 and 7. The aperture 22 is centered on the crack. A tapered plug42, 73 (FIGS. 5 and 8) is formed having dimensions to be received in theaperture 22. After the plug member 42, 73 is brazed to the aperture 22by application of a bonding material and a subsequent heat treatment,the repaired article 10 may be returned to service.

In FIG. 4, the aperture 22 is prepared having sloped sides and an innersurface 26. The intersection of the aperture inner surface 26 and anorthogonal line 28 forms a first included angle 30 for the aperturetaper. An inner side 38 of the article is also illustrated in FIG. 4.The aperture 22 can be formed with an area of reduced wall thicknessafter the location of reduced wall thickness has been determined. Theaperture 22 extends from the article's outer side 34 to the article'sinner side 38.

FIG. 5 illustrates a tapered plug member 42 in side elevation. The plug42 has an inner end 46, an outer end 50, and a plug surface 54. Theintersection of the plug surface 54 and an orthogonal line 58 at theinner end 46 forms a second included angle 62. The first included angle30 and second included angle 62 are substantially equal within a designspecification. The aperture 22 defines a frusto-conical shape, whenviewed in longitudinal section, by virtue of the first included angle 30and the second included angle 62. The larger end of the aperture 22 isdisposed adjacent to the outer side 34. The tapered plug 42 also has afrusto-conical shape, in side elevation, so the tapered plug 42 can bereceived in the aperture 22.

FIG. 6 illustrates a side view of the tapered plug 42 after insertioninto aperture 22. The inner end 46 of the tapered plug 42 extends beyondthe inner side 38 of the article, and the outer end 50 extends beyondthe outer side 34. The inner end 46 and the outer end 50 need not extendbeyond the inner side 38 and the outer side 34, respectively, afterinsertion but may in alternative configurations. For example, an airfoildesign specification can allow a tapered plug 42 to extend up toapproximately about 0.02″ beyond the airfoil's inner side 38. Aprotrusion by the tapered plug 42 of more than about 0.02″ can result inperturbation of the flow of coolant within the airfoil 10, that may setup a site for crevice corrosion. Outer side contours are less of aconcern, as the outer end 50 of a tapered plug 42, can be polished tomatch to the contour of the outer side 34.

With reference to FIG. 6, the plug surface 54 of plug member 42 lies inabutting contact with inner surface 26 of the aperture 22, due toidentical tapers of the plug surface 54 and the inner surfaces of theaperture 22. The local diameter of a taper of each of the plug 42 andaperture 22 is a direct function of length. Thus, pushing the taperedplug 42 into an aperture 22 can result in an increase in local diameter,thus defining an interference fit. The repair process, as embodied bythe invention may include subsequent heat treatment that can relaxstrains in the contacting surfaces. Pushing the tapered plug 42 with arelatively large amount force can cause sufficient interference that nogaps remain between the contacting surfaces. Over-application of aninsertion force on the tapered plug 42 can result in introduction ofsufficient stresses that may introduce micro-cracks in the exteriorwalls of the airfoil proximate the aperture 22. Accordingly, the amountof force used to ensure that the tapered plug 42 is securely insertedinto the aperture 22 is sufficient producing an interference fit bestnot sufficient to introduce cracking.

If the taper of both the plug member 42 and aperture 22 is shallowenough, meaning that the first included angle 30 and the second includedangle 62 are sufficiently small, a high degree of accuracy the nominalinterference can be achieved by measuring the length of the tapered plug42 to be inserted into the aperture 22. A sufficiently shallow taper canbe self-locking, that is, the frictional forces caused by the apertureinner surface 26 and plug surface 54 being pushed together to hold thetapered plug 42 in place, and exceed compressive forces tending to expelthe tapered plug 42 elastically. For example, for nickel-basedsuperalloys, a shallow taper of about 1.20° has been found to beself-locking and further to produce an interference fit of approximatelyabout 0.0012 inches.

The steps in the repair method depicted in FIGS. 1-6 comprise producinga tapered plug 42 and an aperture 22 of equivalent tapers using commonmachining practice. After the aperture 22 and tapered plug 42 have beencreated, the length of the aperture 22, for example the thickness of thewall of the article to be repaired, is measured. The tapered plug 42 isinserted into the aperture 22, using minimal pressure to avoid locking.

After measuring the length of the tapered plug 42 extends beyond thearticle's outer side 34 when the tapered plug 42 is inserted, thetapered plug 42 can be removed from the aperture 22. The tapered plug 42is then cut to length for accurate placement in the aperture 22 soportions of the tapered plug 42 at the inner end 46 and outer end 50 canbe ground or cut-off. Thus the inner end 46 can be at approximately thesame level as the article's inner side 38, and the outer end 50 can beat approximately the same level as the article's outer side 34, once thetapered plug 42 has been inserted again into aperture 22.

If an inner end 46 of a tapered plug 42 projects beyond the article'sinner side 38 or the outer end 50 is to project beyond the article'souter side 34, or both, then the tapered plug 42 can be cut for anydesired degree of interference. In practice, the outer end 50 of thetapered plug 42 extends beyond the article's outer side 34 a relativelysmall amount. A local depression does not result after insertion, due tothe application of force to the outer end 50 of the tapered plug 42during insertion.

Bonding material, such as, at least one of boronized surface treatments,thin sputtered layers of commercial or proprietary braze alloys, anickel layer, and a layer consisting of soft materials, such asaluminum, cobalt, and platinum that will not result in undesirablemetallurgical reactions and some combination thereof can be appliedbetween the aperture inner surface 26 and the tapered plug surface 54the bonding material can be applied before or after insertion of thetapered plug 42 into the aperture 22. For example, the tapered plugsurface 54 can be coated with bonding material prior to insertion intothe aperture 22. Following insertion of the tapered plug 42, the article10 can be heated such that the tapered plug surface 54 is bonded to theaperture inner surface 26.

In an other embodiment as embodied by the invention, the bondingmaterial, for example a braze material, can be added in any spacebetween the article 10 outer side 34, the aperture inner surface 26, andthe tapered plug surface 54. The entire assembly is then heat. The brazematerial move s into vacant spaces therebetween by means of capillaryaction.

An alternative embodiment if the article comprises for directionallyaligned microstructures including as single crystal and directionallysolidified superalloy, microstructures the tapered plug 42 can beprepared from a similar directional material. The matched materialsminimize the amount of grain boundary length created in the plug repairprocess.

With respect to the method illustrated in FIGS. 7-10, the method isuseful for the repair of cast articles having directionally solidifiedmicrostructures. In the method, a curvilinear aperture 22 is prepared inwhich the aperture comprises a pair of intersecting through-holes 23,25. Each hole has different major diameters. The holes 23, 25 areprovided sloping (tapered) side walls 83, 85 to give each through-hole23, 25 a frusto-conical configuration and the advantages as describedabove.

A mating plug member 73 is formed (FIG. 8). The plug member 73 comprisestwo half members 67, 69 each of which are provided with sloping sidewalls 93, 95. Each side wall 93, 95 comprises a taper substantiallyequal to that of side walls 83, 85, to thereby allow mutual overlyingrelation when plug member 73 is inserted in aperture 22. The two halfmembers 67, 69 each comprise different major diameter D₁ and D₂ andprovide mating engagement means. The plug member 73 may only be insertedinto aperture 22 in one orientation. The plug member 73 has adirectionally oriented microstructure, as illustrated in direction ofarrows B—B (FIG. 8), and the oriented microstructure will be closelyaligned with the directional microstructure of the airfoil 10(directional arrows B—B in FIG. 7).

Prior to insertion of the plug member 73 into aperture 22 (FIG. 7), thetapered side walls 93, 95 of plug member 73 may be coated with a bondingmaterial, for example a braze alloy material may be applied afterinsertion of plug member 73 into aperture 22 around the periphery ofsuch aperture 22. The bronze alloy material will flow into the plugmember and aperture interface after heating by capillary action.Thereafter, the airfoil 10 with plug member 73 therein is heated to bondthe sloped wall surfaces 93, 95 to the sloped walls 83, 85. In apreferred embodiment of the method of the present invention(particularly suited to where plug surface 54 of plug member 42 and/oraperture inner surface 26 are first coated with bonding material priorto insertion of plug member 42 into aperture 22). Thereafter, insertionof the plug member 73 is inserted into aperture 22, and a force isapplied to the exterior surface 101 of plug member 73 (see FIG. 10), soas to forcibly insert plug member 48 into aperture 22 and cause aninterference fit “i”(see FIG. 10) between the half members 67, 69 ofplug member 73 and the through-holes 23, 25 that comprise aperture 22.The interference fit may be pre-determined in the manner previouslydescribed. Subsequent heat treatment may be used before, after, orduring the bonding step so as to effect stress relief.

EXAMPLE

An aperture 22 of 0.15 inches diameter on the outer wall 34 of a turbineblade 10 is created, having side walls 26 and an included angle 30 of1.2°, wherein the wall thickness is about 0.08 inches plus or minusabout 0.02 inches (See FIG. 4). A plug member 50, having similarlysloped side walls 54 of 1.20° (see included angle 62 of FIG. 5) isprepared, and is uniformly coated with commercially braze alloy. Plug 42is placed into aperture 22, so as to rest against side walls 26 ofaperture 22 (See FIG. 4). Plug member 42 is thereafter pushed atranslational distance of about 0.50 inches into aperture 22, creatingabout 0.0012 inch interference (i.e. about 0.050 xtan 1.2°). Due to theshallow taper, such interference is self-locking. The plug member 42 isthereafter heated to allow the side walls 54 thereof to be brazed toaperture side walls 26.

While various embodiments are described herein, it will be appreciatedfrom the specification that various combinations of elements, variationsor improvements therein may be made by those skilled in the art, and arewithin the scope of the invention.

We claim:
 1. A mating plug member for filling an aperture in a castarticle, said mating plug member comprising mating engagement means formatingly engaging and allowing insertion of said mating plug memberwithin said aperture upon alignment of said mating plug member.
 2. Themating plug member according to claim 1, wherein said mating plug memberis formed from a superalloy.
 3. The mating plug member according toclaim 2, wherein said superalloy is a nickel-base superalloy.
 4. Themating plug member according to claim 2, wherein said mating plug memberhas a directionally oriented microstructure and growth axis.
 5. Themating plug member according to claim 1, wherein said engagement meanscomprises a first half member and a second half member, wherein each ofsaid first and said second half member has sloping side walls, andwherein said first half member has a first diameter and said second halfmember has a second diameter different from said first diameter formatingly engaging and allowing insertion of said mating plug memberwithin said aperture upon alignment of said mating plug member.
 6. Acast article, said cast article comprising: a) at least one wall formedfrom a superalloy, said at least one wall having a thickness; b) anaperture extending through said wall, wherein said aperture has slopedside walls; and c) a mating plug member formed from a second superalloyand disposed in said aperture, said mating plug member comprising matingengagement means for matingly engaging and allowing insertion of saidmating plug member within said aperture upon alignment of said matingplug member, and wherein said sloping side walls of said first halfmember and said second half member mutually overlie and evenly abut saidsloped side walls of said aperture.
 7. The cast article according toclaim 6, wherein said superalloy and said second superalloy havesubstantially the same composition.
 8. The cast article according toclaim 7, wherein said superalloy is a nickel-base superalloy.
 9. Thecast article according to claim 7, wherein each of said at least onewall of said cast article and said mating plug member have adirectionally oriented microstructure and growth axis, and wherein saiddirectionally oriented microstructure and growth axis of said at leastone wall is aligned with said directionally oriented microstructure andgrowth axis of said mating plug member when said mating plug member isinserted in said aperture.
 10. The cast article according to claim 6,wherein said at least one wall of said cast article has a thickness ofbetween about 0.06 inch and about 0.10 inch.
 11. The cast articleaccording to claim 6, wherein said aperture is located on a sitepreviously in contact with a ceramic bumper.
 12. The cast articleaccording to claim 6, wherein an end of said mating plug member extendsbeyond one of an inner surface and an outer surface of said at least onewall.
 13. The cast article according to claim 12, wherein an end of saidmating plug member extends up to about 0.02 inch beyond one of an innersurface and an outer surface of said at least one wall.
 14. The castarticle according to claim 6, wherein an end of said mating plug memberis substantially level with one of an inner surface and an outer surfaceof said at least one wall.
 15. The cast article according to claim 6,wherein said plug member is joined to said at least one wall byself-locking fit between said sloped side walls of said aperture andsaid sloping side walls of said mating plug member.
 16. The cast articleaccording to claim 6, further including a bond material disposed betweensaid sloped side walls of said aperture and said sloping side walls ofsaid mating plug member, wherein said bond material joins said matingplug member to said at least one wall of said cast article.
 17. The castarticle according to claim 16, wherein said bond material comprises aboronized surface treatment.
 18. The cast article according to claim 16,wherein said bond material comprises nickel.
 19. The cast articleaccording to claim 16, wherein said bond material comprises a braze. 20.The cast article according to claim 16, wherein said bond materialcomprises one of aluminum, cobalt, platinum, and combinations thereof.21. The cast article according to claim 6, wherein said cast article isan airfoil.
 22. The cast article according to claim 6, wherein saidmating engagement means comprises a first half member and a second halfmember, wherein each of said first and said second half member hassloping side walls, and wherein said first half member has a firstdiameter and said second half member has a second diameter differentfrom said first diameter for matingly engaging and allowing insertion ofsaid mating plug member within said aperture upon alignment of saidmating plug member.